1. Field of the Invention
This invention relates to a resin composition for use in molding articles by injection molding requiring light-shielding property used for photographic photosensitive materials. More particularly, this invention relates to a resin composition for the articles, such as instant film pack, spool for photographic film, photographic film cartridge, container for strip materials and sheets for loading in a light room, photographic film camera, lens attached film and magazine for 8 mm film.
2. Description of the Prior Art
Such molded articles were usually composed of high-impact polystyrene resin blended with carbon black for securing light-shielding and synthetic rubber such as butadiene rubber for reinforcement. While, in the case of requiring particular strength or heat resistance, ABS resin was employed. These molded articles are disclosed, for example, in Japanese Patent KOKOKU No. 56-16414, Japanese Patent KOKAI Nos. 57-207248, 58-203437, 60-14237 and 61-48841 and Japanese Utility Model KOKAI Nos. 61-86367 and 61-128256.
The above molded articles are required to be positioned accurately and to be flat at the focal plane, and therefore, the materials composing these articles are necessary to have a small contraction coefficient and the rigidity capable of resisting deformation. Besides, in the case of the core for photographic photosensitive strip material, the spool for photographic film and the like, accuracy to size is required for securing loading ability of photographic film in camera and light-shielding, and furthermore, wear resistance and slipping character are also required because of rotating in camera. In the case of photographic film camera and the film pack used for instant photographic system, accuracy to size, wear resistance and slipping character are required similarly, and physical strength is also necessary in order to prevent fogging of the film by broken. Since these molded articles are occasionally used out of doors in the sunshine or left in a car, heat resistance and impact strength particularly at a low temperature are also necessary.
However, the above high-impact polystyrene resin blended with carbon black is insufficient in heat resistance and impact strength. For example, when the molded article was left in a car sunshined in summer, it was sometimes deformed to interfere with its usability. Moreover, the slipping character is also insufficient, even though an usual commercial lubricant is blended. Therefore, it has been reported that the slipping character is secured by coating at least one of the surfaces to contact with each other of the spool and the cap of a photographic film cartridge with a lubricant such as wax, paraffin oil, higher fatty acid ester or silicone (Japanese Utility Model KOKAI No. 53-155638).
The article composed of the ABS resin blended with carbon black is sufficient in most of the necessary properties other than slipping character. However, it is expensive and injection moldability of this resin is inferior.